U.S. patent number 6,222,370 [Application Number 09/267,040] was granted by the patent office on 2001-04-24 for universal battery monitor.
Invention is credited to Brian Walter Schousek, Theresa Jean Schousek.
United States Patent |
6,222,370 |
Schousek , et al. |
April 24, 2001 |
Universal battery monitor
Abstract
The invention includes a direct current energy source monitor
which automatically detects the nominal voltage of the direct
current energy source to which it is attached. The invention
further includes a direct current energy source monitor which is
self-powered from the direct current energy source being monitored.
The multiple nominal voltage direct current energy source monitor
includes an analog-to-digital converter configured to measure
voltage from a direct current energy source being monitored and
generate a digital output corresponding thereto. The apparatus
includes a programmable control device configured to receive the
digital output from the analog-to-digital converter and to look up
a nominal voltage corresponding to the digital output, and is
further configured to calculate a relative charge of the direct
current energy source as compared to a full charge on the direct
current energy source. The direct current energy source monitor can
include a voltage controlled oscillator configured to receive the
voltage of the direct current energy source being monitored and
generate a frequency output proportional to the received voltage.
The programmable control device is configured use the frequency
output to determine the received voltage from the direct current
energy source. The direct current energy source monitor preferably
includes a calibration circuit configured to periodically calibrate
the voltage controlled oscillator. The calibration circuit is
configured to generate known voltages which are supplied to the
voltage controlled oscillator. The voltage controlled oscillator is
governed by a transfer function, wherein its output is a function
of the input. The coefficients of the transfer function are
calculated by the programmable control device based on the known
voltages applied to the voltage controlled oscillator and the
output produced by the voltage controlled oscillator in response
thereto.
Inventors: |
Schousek; Brian Walter
(Houlton, WI), Schousek; Theresa Jean (Houlton, WI) |
Family
ID: |
26759898 |
Appl.
No.: |
09/267,040 |
Filed: |
March 13, 1999 |
Current U.S.
Class: |
324/436;
320/136 |
Current CPC
Class: |
G01R
31/3835 (20190101); G01R 31/3648 (20130101); G01R
31/006 (20130101) |
Current International
Class: |
G01R
31/36 (20060101); G01R 31/00 (20060101); G01N
027/416 () |
Field of
Search: |
;324/436,433,430,427
;320/136,161,134 ;429/90,91,92 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wong; Peter S.
Assistant Examiner: Luk; Lawrence
Attorney, Agent or Firm: Reidlaw, L.L.C. Reid; John S.
Parent Case Text
RELATED CASES
This application claims priority to Provisional Patent Application
Ser. No. 60/077,964, filed Mar. 13, 1998, and which is incorporated
herein by reference.
Claims
We claim:
1. A multiple nominal voltage direct current energy source monitor,
comprising:
an analog-to-digital converter configured to measure voltage from a
direct current energy source being monitored by the voltage monitor
and generate a digital output corresponding thereto; and
a programmable control device configured to receive the digital
output from the analog-to-digital converter and to look up a
nominal voltage from a range of nominal voltages anticipated to be
encountered by the direct current energy source monitor, the
nominal voltage corresponding to the digital output, and further
configured to calculate a relative charge of the direct current
energy source as compared to a full charge on the direct current
energy source.
2. The multiple nominal voltage direct current energy source
monitor of claim 1 further comprising a display in communication
with the programmable control device and configured to display at
least one of the nominal direct current energy source voltage or
the relative charge of the direct current energy source.
3. The multiple nominal voltage direct current energy source
monitor of claim 1 further comprising a voltage controlled
oscillator configured to receive the voltage of the direct current
energy source being monitored and generate a frequency output
proportional to the received voltage, and further wherein the
programmable control device is configured to use the frequency
output to determine the received voltage from the direct current
energy source.
4. The multiple nominal voltage direct current energy source
monitor of claim 3 wherein the voltage controlled oscillator is
comprised of precision circuit components.
5. The multiple nominal voltage direct current energy source
monitor of claim 3 further comprising a calibration circuit
configured to periodically calibrate the voltage controlled
oscillator.
6. The multiple nominal voltage direct current energy source
monitor of claim 3 wherein the voltage controlled oscillator
comprises a first op-amp configured to receive the voltage of the
direct current energy source being monitored and generate an output
in response thereto, a second op-amp configured to receive the
output from the first op-amp and generate a second output in
response thereto, the second output being the frequency output
proportional to the received voltage.
7. The multiple nominal voltage direct current energy source
monitor of claim 6 wherein voltage controlled oscillator further
comprises a resistor array forming feedback elements to the first
and second op-amps.
8. The multiple nominal voltage direct current energy source
monitor of claim 5 wherein the calibration circuit is configured to
receive a first predetermined voltage from the programmable control
device and generate a first predetermined output in response
thereto, and wherein the voltage controlled oscillator is further
configured to receive the first predetermined output and generate a
first output frequency in response thereto.
9. The multiple nominal voltage direct current energy source
monitor of claim 8 wherein the voltage controlled oscillator (VCO)
is comprised of VCO circuit components, wherein the generation of
the output frequency by the voltage controlled oscillator is
governed by the transform function y=mx+b, and wherein y indicates
the frequency output of the voltage controlled oscillator, x
indicates the input to the voltage controlled oscillator, and m and
b are coefficients particular to the VCO circuit components, and
wherein the programmable control device is further configured to
use the first predetermined voltage and the first output frequency
to calculate the coefficients m and b.
10. The multiple nominal voltage direct current energy source
monitor of claim 9 wherein the calibration circuit is configured to
receive a second predetermined voltage from the programmable
control device and generate a second predetermined output in
response thereto, and wherein the voltage controlled oscillator is
further configured to receive the second predetermined output and
generate a second output frequency in response thereto.
11. The multiple nominal voltage direct current energy source
monitor of claim 10 wherein the programmable control device is
further configured to use the second predetermined voltage and the
second output in response thereto to calculate the coefficients m
and b.
12. The multiple nominal voltage direct current energy source
monitor of claim 11 wherein the programmable control device is
configured to periodically generate the first and second
predetermined voltages to cause the voltage controlled oscillator
to generate the first and second output frequencies in response
thereto.
13. The multiple nominal voltage direct current energy source
monitor of claim 12 wherein the programmable control device is
further configured to use the calculated values for coefficients m
and b to calibrate the output of the voltage controlled oscillator
according to the equation y=mx+b, and further wherein the
programmable control device is further configured to use the
calculated values of m and b to determine the voltage detected by
the voltage controlled oscillator from the direct current energy
source to calculate the voltage of the direct current energy
source.
14. The multiple nominal voltage direct current energy source
monitor of claim 1 wherein the programmable control device is
provided with a look-up table of voltages corresponding to nominal
voltages expected to be encountered by the direct current energy
source voltage monitor, and to indicate which of the nominal
voltages corresponds to the detected voltage of the direct current
energy source.
15. The multiple nominal voltage direct current energy source
monitor of claim 14 wherein the programmable control device is
provided with a look-up table of threshold voltages corresponding
to defined direct current energy source charge amounts.
16. The multiple nominal voltage direct current energy source
monitor of claim 15 wherein the threshold voltages in at least the
look-up table of voltages corresponding to nominal voltages
expected to be encountered by the direct current energy source
voltage monitor or the look-up table of threshold voltages
corresponding to defined direct current energy source charge
amounts can be set by a user of the direct current energy source
voltage monitor.
17. The multiple nominal voltage direct current energy source
monitor of claim 8 wherein the programmable control device
comprises random access memory (RAM), read only memory (ROM), a
computation component configured to perform mathematical
calculations, and a counter configured to count pulses.
18. A multiple nominal voltage direct current energy source
conductance monitor for monitoring a direct current energy source,
comprising:
an analog-to-digital converter configured to measure conductance of
a direct current energy source being monitored by the conductance
monitor and generate a digital output signal corresponding thereto;
and
a programmable control device configured to received the digital
output signal from the analog-to-digital converter and to look up a
nominal conductance from a range of nominal conductances
anticipated to be encountered by the direct current energy source
conductance monitor, the nominal conductance corresponding to the
digital output signal, and further configured to calculate a
relative state-of-health of the direct current energy source
relating to at least one of age, charge capacity, or capability for
instantaneous current supply of the direct current energy source as
compared to a nominal direct current energy source.
19. The multiple nominal voltage direct current energy source
conductance monitor of claim 18 further comprising a display in
communication with the programmable control device, the display
configured to display the nominal direct current energy source
conductance.
20. The multiple nominal voltage direct current energy source
conductance monitor of claim 18 further comprising a display in
communication with the programmable control device, the display
being to display the relative state-of-health of the direct current
energy source.
21. The multiple nominal voltage direct current energy source
conductance monitor of claim 18 further comprising a dynamic
conductance measurement circuit.
22. The multiple nominal voltage direct current energy source
conductance monitor of claim 18 further comprising a small-signal
alternating current generator and a small-signal alternating
current measurement circuit.
23. Method for determining a nominal voltage of a direct current
energy source having a charge, comprising:
providing a programmable control device having stored ranges of
numbers, each range corresponding to an associated nominal direct
current energy source voltage anticipated to be encountered, the
programmable control device further including a series of machine
executable steps for comparing a received signal to the stored
ranges of numbers to identify an associated nominal direct current
energy source voltage;
measuring the charge on the direct current energy source;
generating a signal based on the charge measured on the direct
current energy source;
providing the signal to the programmable control device;
looking up from the stored ranges of numbers a nominal direct
current energy source voltage which is associated with the signal;
and
receiving an output from the programmable control device indicative
of the nominal voltage of the direct current energy source.
24. The method of claim 23 further comprising providing a voltage
controlled oscillator to generate the signal.
25. The method of claim 24 further comprising periodically
calibrating the voltage controlled oscillator.
26. The method of claim 25 further comprising automatically
calibrating the voltage controlled oscillator by causing the
programmable control device generate a first, periodic known
signal, providing the first, periodic known a signal to the voltage
controlled oscillator, and using the signal generated by the
voltage controlled oscillator in response thereto to calibrate the
voltage controlled oscillator.
27. In the method of claim 23 wherein the programmable control
device is further provided with a set of values within each range
of numbers, each set of values being indicative of the amount of
charge on the direct current energy source for the nominal direct
current energy source voltage associated with the range of numbers,
and wherein the programmable control device is further provided
with a series of machine executable steps for comparing the signal
to the set of values within the range of numbers ranges
corresponding to the identified associated nominal direct current
energy source voltage to identify relative charge on the direct
current energy source, and wherein the method further comprises
receiving a second output provided from the programmable control
device indicative of the relative charge on the direct current
energy source.
Description
FIELD OF THE INVENTION
This invention pertains to energy source monitors, and in
particular to a direct current energy source monitor capable of use
with a plurality of different DC energy sources, such as batteries,
wherein the energy sources have different nominal voltages from one
another.
BACKGROUND
Direct current (DC) energy sources, such as batteries, are used in
many situations where constant alternating current (AC) power is
not available. Examples include auxiliary power for vehicles such
as semi trucks, automobiles, ambulances, motorcycles, recreational
vehicles, boats, and standby generators. Examples further include
primary power for forklifts, trolling motors, golf carts, pallet
trucks, floor scrubbers, wheel chairs, electric vehicles, and
scissor lifts. The primary DC energy source used in such
applications is a lead acid battery, typically ranging in nominal
voltage from 6 to 48 volts.
In many applications, it is desirable or even critical to monitor
the charge level of the energy source so that the user has an
indication when the energy source is getting low on voltage or is
deviating from a desired voltage range, and needs to be recharged
or replaced. The voltage level on the energy source is a measurable
indicator of charge of the energy source, and can be monitored with
a device commonly known as a "monitor" or a "battery monitor" where
the source is a battery. Without a monitor, typically the only
inherent indication that a user has that the energy source is in a
charged state is whether or not it activates the equipment to which
it is attached. Many prior art devices exist which measure the
voltage level on a battery or other DC energy source and display
the charge level through some means (e.g., bar graph, digit
readout, mechanical meter) but these devices generally work only
for a particular nominal energy source voltage. That is, a prior
art 12 volt DC source monitor will not properly monitor, or even
work on, a nominal 24 volt energy source. Further, prior art DC
monitors often require supplemental power besides the source being
monitored in order to operate. The ability for a prior art monitor
to work for a plurality of nominal source voltages generally
requires some user interaction, for example, turning a knob to
select a voltage, reading a printed conversion table, etc. A normal
prior art single-voltage DC energy source monitor is typically
constructed of a circuit which essentially is a set of voltage
level comparators, with the thresholds for the comparators tied to
some reference voltage and the output tied to a display device such
as a light emitting diode (LED). This solution is impractical for a
multiple-voltage DC monitor because with each type of DC source a
complete set of comparators and associated reference thresholds
must be included which eventually lead to a large, expensive
circuit.
In many applications, it is desirable to monitor the direct current
(DC) energy source capacity, aging characteristics, or capability
of instantaneous current supply, commonly known as the DC energy
sources' "condition" or "state-of-health." The conductance of a
battery is a measurable indicator of the "state-of-health", and can
be tested and/or monitored with a device commonly known as a
"battery monitor."
It is thus desirable that a DC energy source voltage monitor be
provided which has the capability to automatically determine
nominal voltages of the batteries intended for monitoring by the
device, and which is relatively simple to manufacture. In addition,
it is desirable to be able to monitor the state of health or
battery condition, which can be indicated by conductance of the DC
source.
SUMMARY OF THE INVENTION
The invention includes a DC energy source monitor (which will be
known simply as a "monitor" herein for the sake of simplicity),
such as a battery monitor, which automatically detects the nominal
voltage of the DC energy source to which it is attached. It is
understood that when the expression "battery monitor" is used
herein with reference to the invention, that it includes more
broadly a monitor for monitoring any source of direct current
energy, and should not be considered as limited to a battery unless
expressly stated as being so limited. The invention further
includes a monitor which is self-powered from the DC source being
monitored. In a first embodiment of the invention, a multiple
nominal voltage monitor comprises an analog-to-digital converter
configured to measure voltage from a DC source being monitored by
the voltage monitor and generate a digital output corresponding
thereto. The embodiment further includes a programmable control
device configured to receive the digital output from the
analog-to-digital converter and to look up a nominal voltage
corresponding to digital output, and further configured to
calculate a relative charge of the DC source as compared to a full
charge from the nominal DC source. The first embodiment of the
invention can further include a display in communication with the
programmable control device and configured to display the nominal
DC source voltage and the relative charge of the DC source as
compared to a fully charged nominal source.
A second embodiment of the invention comprises the components of
the first embodiment, and further comprises a voltage controlled
oscillator configured to receive the voltage of the DC source being
monitored and generate a frequency output proportional to the
received voltage. The programmable control device is configured use
the frequency output to determine the received voltage from the DC
source.
In yet a third embodiment of the invention, a multiple nominal
voltage DC energy source voltage monitor comprises the components
of the first and second embodiments, and further comprises a
calibration circuit configured to periodically calibrate the
voltage controlled oscillator. The calibration circuit is
configured to generate known voltages which are supplied to the
voltage controlled oscillator. The voltage controlled oscillator is
governed by a transfer function, wherein its output is a function
of the input. The coefficients of the transfer function are
calculated by the programmable control device based on the known
voltages applied to the voltage controlled oscillator and the
output produced by the voltage controlled oscillator in response
thereto.
The invention further comprises a DC energy source voltage monitor
which is powered by a power supply which is powered by the DC
source being monitored. The power supply comprises a series voltage
regulator utilizing a voltage reference with a power pass
transistor.
The invention can further include a multiple nominal voltage direct
current energy source monitor for monitoring the state of health of
the energy source, including conductance, age, capability of the
source to provide current, and charge capacity of the source.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an environmental view showing a DC energy source monitor
of the present invention connected to a direct current energy
source.
FIG. 2 is a schematic circuit diagram showing a power circuit which
can be used in the present invention.
FIG. 3 is a schematic circuit diagram showing a display circuit
which can be used in the present invention.
FIG. 4 is a schematic circuit diagram showing a voltage controlled
oscillator circuit which can be used in the present invention.
FIG. 5 is a schematic circuit diagram showing a calibration circuit
which can be used in the present invention.
FIG. 6 is a schematic circuit diagram showing a control section
circuit which can be used in the present invention.
FIG. 7 is a flow chart showing the logic of a control scheme which
can be used in the present invention.
FIG. 8 is a block diagram showing the interaction of the circuit
diagrams of FIGS. 2 through 6.
FIG. 9 is a schematic circuit diagram showing a prior art DC energy
source monitor.
FIG. 10 is a schematic circuit diagram showing a circuit which can
be used to change the threshold levels of relative charge as
detected by the DC energy source monitor.
FIG. 11 is a schematic circuit diagram of a circuit which can be
used with the monitor of the present invention to also monitor
conductance of a DC energy source.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
The present invention pertains to a direct current (DC) energy
source monitor. A typical example of a DC energy source is a
battery. It is understood that the present invention pertains to
the broader category of DC energy sources, even if reference is
made to a "battery". The present invention will be described herein
simply as a "monitor", a "source monitor", a "DC source monitor", a
"DC energy source monitor", a "direct current energy source
monitor", or a "battery monitor", in all cases referring to the
same thing. Likewise, the source being monitored will be referred
to alternately as a "direct current energy source", a "DC energy
source", a "DC source", a "source", or a "battery", in all cases
referring to the a direct current energy source, unless expressly
limited to a particular type of direct current energy source.
Examples of DC sources include a single battery cell, a bank of
batteries, a set of batteries in series, or a DC source converted
from an alternating current (AC) source .
While the present invention pertains to a monitor for monitoring
voltage of a source. it also pertains to a monitor for monitoring
the state of health, or present condition, of the source. Examples
of state-of-health of a DC source, such as a battery, include the
conductance of the source, the age of the source, the charge
capacity of the source, and the capability of the source to provide
instantaneous current supply. Thus, while the monitor may be
referred to herein from time to time as a "voltage monitor", it is
understood that the monitor can also comprise a state-of-health DC
energy source monitor.
The monitor of the present invention can be used to monitor a
loaded or an unloaded source. Further, the present invention can be
used either as a continuous monitor, or as an intermittent monitor
or tester. The expression "monitor" should be understood as
encompassing both continuous and intermittent monitors.
In a first embodiment of the invention, the input from the DC
source being monitored is measured directly with an
analog-to-digital converter (ADC) to produce a converted, digital
signal. The converted digital signal is then provided to a
microcontroller (uC) which is configured with a look-up table to
determine the nominal voltage of the source to which the monitor is
attached. The microcontroller can then be programmed to select the
corresponding nominal voltage, and to activate appropriate, known,
circuitry for monitoring a source of the indicated nominal voltage.
The indicated voltage can be further displayed to the user, in
addition to displaying the actual, monitored voltage level of the
source. The first embodiment is based on the principle that most DC
energy sources, such as lead-acid batteries, are constructed such
that their charge levels do not overlap. For example, the voltage
of a nominal 24 volt battery, even at its most discharged state, is
generally greater than the voltage of a highly charged 12 volt
battery. It is therefore possible to distinguish between 6, 12, 24,
36 and 48 volt batteries or sources and select their charge levels
with a software lookup table. This first embodiment will be known
as the "Microcontroller Based Analog to Digital Converter
Embodiment" or "ADC Embodiment" for reference purposes herein
only.
A second embodiment, which will be referred to herein for reference
purposes only as the "Microcontroller Based Voltage Controlled
Oscillator Embodiment" or "VCO Embodiment", improves on the
resolution of the ADC Embodiment. In order to repeatedly measure,
for example, the difference between a discharged and 25% charged 12
volt DC source, the ADC Embodiment is preferably configured to
distinguish levels of 120 millivolts. The ADC Embodiment is also
preferably configured to be able to operate over sufficient range
to allow for a fully charged 48 volt DC source (for example, four
batteries at 12.63 volts per battery placed in series for a total
voltage of 50.52V). Assuming the complete range of operation to be
40 volts, the ADC Embodiment is preferably configured to have a
minimum resolution of 40 volts divided by 0.120 volts per count, or
333 counts for full scale. This is slightly more than a typical
8-bit ADC can accomplish, and in practice more bits of resolution
are desirable to provide noise immunity. ADCs greater than 8 bits
are available, but provide complexity to the ADC Embodiment.
In the second embodiment, the VCO Embodiment, the input voltage
from the DC source being monitored is first converted into a
frequency using a voltage controlled oscillator ("VCO"), and then a
microcontroller is used to measure the frequency produced by the
VCO. The microcontroller is configured to make a determination of
what type of DC source (nominal voltage) is attached to the monitor
based on the measured frequency. The microcontroller can then be
configured to set the output display accordingly, and to activate
other known circuitry for monitoring the DC source voltage. The
voltage-to-frequency conversion performed in the second embodiment
improves on the accuracy of the ADC embodiment. In the VCO
embodiment, the frequency generated is preferably repeatable for
the voltage levels of interest. This can be accomplished by using
high precision components within the circuitry of the VCO
Embodiment of the monitor.
A third embodiment of the present invention obtains the accuracy of
the second embodiment, without the use of precision circuit
components in the voltage control oscillator. This third
embodiment, which is the preferred embodiment of the present
invention, will also be referred to herein, for reference purposes
only, as the "Microcontroller Based VCO Implementation with
Self-Calibration Embodiment".
Using high precision components in the VCO in the second embodiment
provides for an accurate circuit output. If high precision
components are not used in the VCO, then the output thereof can
deteriorate. In order to avoid using high precision components in
the VCO, a method and apparatus for calibrating the VCO is
provided. In a first variation, the apparatus for calibrating the
VCO is accomplished by the addition of variable resistors in the
VCO. The variable resistors arc adjusted using known circuit design
methods until the variation in the output of the VCO is nullified.
In a second, preferred variation on the third embodiment, a
microcontroller is used to calibrate the VCO. Since the second
embodiment preferably incorporates a microcontroller in the system
to distinguish the voltage levels, the microcontroller (MC) can
also be used to provide self-calibration of the VCO. The VCO of the
third embodiment provides for a very linear output from the VCO,
and aids in the self-calibration effort.
The Apparatus
Turning to FIG. 1, an environmental view of an apparatus of the
present invention is shown. A DC energy source monitor 10,
constructed in accordance with the present invention, monitors the
voltage of a DC energy source, here shown as a battery 9. The
voltage monitor 10 has a first contact 11 connected to the positive
terminal of the source, and a second contact 12 connected to the
negative lead of the DC source. The monitor 10 has 5 light emitting
diodes (LEDs) 20 which are used to display the nominal voltage of
the source being monitored, as well as the relative charge on the
source as compared to a "full" charge from a nominal source of the
same type.
Apparatus Overview
A schematic block diagram of one implementation of the third
embodiment of the present invention is shown in FIG. 8. FIG. 8
shows the various components which make up this particular
implementation. The monitor 10 includes a power supply circuit 30.
The power supply circuit 30 is configured to convert power from the
DC source being monitored, such as battery 9, into power used by
the monitor itself. This results in a "self powered" voltage
monitor, not requiring auxiliary power. The monitor 10 further
includes a display circuit 40 for displaying the remaining charge
on the battery, as well as displaying the nominal voltage of the
battery being monitored.
The DC source monitor 10 of FIG. 8 includes a voltage controlled
oscillator (VCO) circuit 50 for providing a digital signal to a
microcontroller 70, which then determines the nominal voltage of
the source being monitored based on the frequency of the digital
output from the VCO circuit 50. The monitor 10 also preferably
includes the calibration circuit 60 which calibrates the VCO
circuit 50. The output VCO OUT from the VCO circuit 50 is provided
to the microcontroller 70, which then provides a calibration signal
VCO-CAL to the calibration circuit 60. Based on the calibration
signal, the calibration circuit calibrates the VCO circuit 50 with
a calibrated signal VCO-IN.
The apparatus can further include the conductance module 80 for
monitoring the state of health or condition of the DC source.
The circuit components will be more fully described below.
Power Supply
Turning to FIG. 2, one example of a power supply circuit 30 which
can be used for a battery monitor of the present invention is
shown. The power supply circuit is connected to the source being
monitored at contacts 11 and 12, as shown in FIG. 1. The output
from the power supply circuit is VPWR. The power supply circuit
comprises a series voltage regulator utilizing a voltage reference
32 with a power pass transistor Q3. In one example the voltage
reference 32 used is a standard ZR431 voltage reference.
The operation of the power supply circuit 30 is similar to that
described further herein for the calibration circuit 60, with the
exception that the voltage reference 32 in the power supply circuit
30 controls the base of the transistor Q3 to the source current
rather than shunting current away from a higher level of source
current. Since the input voltage from the source being monitored
can be as high as 50 volts in certain instances, with a desired
output voltage of 3V from the power supply circuit 30 and maximum
current of 20 mA, the power dissipated in the pass transistor Q3
can be as high as 1.5 watts. This figure can be used to select the
remaining components for the circuit. Typically however, the
current from the power supply circuit 30 is less than 20 mA.
The specific power supply circuit 30 shown in FIG. 2 is an
exemplary power circuit for a voltage monitor designed to monitor
DC energy sources having nominal voltages of 6 to 48 volts.
Further, the specific power supply circuit 20 shown in FIG. 2 is
designed to provide a power of 3V to the rest of the monitor.
Accordingly, the additional components of the power circuit 30
shown in FIG. 2, including resistors R10, R13, R14, and R15,
capacitors C1 and C3, and diode D1, are shown with exemplary design
values for the particular example of power supply circuit
described. For DC voltage monitors designed to monitor a different
range of nominal voltages, or to provide a different voltage to the
other circuits of the monitor, the values for these components can
be selected using known circuit design techniques.
Display
Turning to FIG. 3, an exemplary circuit diagram of a display
circuit 40 which can be used in the present invention is shown. The
particular display circuit shown uses LEDs to display the output.
It is understood than an LCD display, or a meter or a digital
readout can also be provided according to known techniques for
displaying outputs from digital circuits. For example, an LCD
display showing actual numerical values can be used in place of the
LED indicator lights shown in the figure. The embodiment shown in
FIG. 2 provides a relative simple, easy to implement, low power
implementation.
The exemplary display circuit shown consists of five 5 LEDs,
indicated as D6 (red), D3 (yellow 1), D2 (yellow 2), D4 (green 1),
and D5 (green 2). The activation of the LEDs is driven by the
microcontroller 72 of FIG. 6, as indicated in FIG. 8. In the
example shown, the five LEDs indicate nominal relative source
charge, as compared to a full charge on the nominal source, of 0%,
25%, 50%, 75% and 100%, as indicated in FIG. 1. For example, if the
first yellow LED D3 were lit continuously, it would indicate a
remaining battery life of 25% of full charge. In practice, the
actual thresholds upon which the LEDs are activated can be
configured to activate the LEDs at the midpoints between the levels
of 0-25%, 25-50%, 50-75%, and 75-100%. In such instance a lit red
LED D6 indicates less than 12.5% percent of full battery capacity,
and green 2 (D4) indicates greater than 87.5% of full battery or
source capacity.
In addition to a continuously lit LED indicating relative source
charge, a blinking LED can indicate which DC source type (nominal
voltage) is being monitored, as indicated in FIG. 1. The
appropriate LED blinks when the unit powers on and any time a
different DC energy source type is connected to the monitor. The
LEDs shown in FIGS. 1 and 3 correspond to nominal voltages as
follows: D6 (red) for 6V, D3 (yellow 1) for 12V, D2 (yellow 2) for
24V, D4 (green 1) for 36V, and D5 (green 2) for 48V. The activation
of a blinking LED is controlled by the microcontroller 72 of FIG. 6
using known techniques for configuring a microcontroller to
activate an LED in a continuous or blinking fashion upon receipt of
a given digital input signal.
The values for resistors R16, R2 and R1 of FIG. 3 are exemplary for
the particular implementation shown and described herein.
In one variation on the display circuit shown, the LEDs can be
pulsed rather than turning them on by direct current, which can
reduce current consumption within the display section 40 of the
monitor 10.
Voltage Controlled Oscillator
Turning to FIG. 4, an exemplary voltage controlled oscillator (VCO)
circuit 50 which can be used in the present invention is shown. The
voltage controlled oscillator shown comprises of a dual op-amp (52
and 54) with a resistor array (R9A through R9H) forming feedback
elements, a capacitor C2 for timing, and a MOSFET Q2 for changing
the output polarity. The VCO section 50 shown in FIG. 4 is
configured to produce a fixed 50% duty cycle regardless of the
frequency generated. For the purposes of the VCO used in the
specific embodiment of the monitor 10 described herein, it is
assumed that the output of the VCO circuit 50 is linear and of the
form y=m*x+b, where x is the input voltage VCO-IN, and y is the
output frequency VCO-OUT. By using precision circuit components for
the VCO circuit 50, the constants m and b can be held relatively
constant.
However, where precision circuit components are not used for the
VCO circuit 50, m and b are assumed to be stable over short time
durations, but not over temperature and component variations. That
is, if precision circuit components are not used for the VCO
circuit 50, m and b can change from monitor to monitor and in a
given monitor over temperature. To compensate for this variation,
instead of relying on many precision components in the VCO
circuitry 50, the third embodiment of the DC source monitor is
configured to use a small number of precision components in a
calibration circuit 60 (discussed more fully below) to calibrate
the VCO using periodic in-line calibration to compensate for
variations in the VCO circuit 50. The calibration circuit 60 can be
used in conjunction with the microcontroller 72 to calculate values
for m and b, as will be described more fully below.
As indicated in FIG. 8, the VCO circuit 50 receives power from the
power supply circuit 30, a calibrated signal VCO-IN from the
calibration circuit 60, and provides output VCO_OUT to the
microcontroller 70. The output of the VCO circuit VCO_OUT is a
digital signal indicative of the frequency (as counted by square
waves generated by the VCO) generated by the VCO. The frequency
generated by the VCO is dependent upon the load connected to the
monitor, i.e., the voltage of the DC source being monitored. In the
second embodiment of the invention wherein no calibration circuit
60 is used, the VCO receives as VCO-IN the input INPUT directly
from the positive terminal of the source 9 (see FIG. 8), and
circuit calibration 60 is removed.
The values and selection of the particular circuit components for
the VCO circuit 50 shown in FIG. 4 are exemplary only.
VCO Calibration
In the third embodiment or preferred of the invention, the monitor
10 is provided with a VCO calibration circuit 60 as shown in FIG.
8. A schematic circuit diagram of one implementation of the
calibration circuit 60 is shown in FIG. 5. Turning now to FIG. 5,
the VCO calibration circuit 60 receives as an input INPUT, the raw,
unregulated voltage input from the positive terminal of the DC
source 9 being monitored by the monitor 10, as shown in FIG. 8. The
output VCO-IN of the calibration circuit 60 is the calibrated
voltage provided to the VCO circuit 50, as indicated in FIG. 8. For
a monitor configured to monitor DC sources such as batteries having
nominal voltages of between 6V and 48V, and operating on a 3V power
supply, the output voltage VCO-IN from the calibration circuit 60
preferably varies from approximately 0.88V to 7.7V.
The calibration circuit 60 includes a voltage reference 62, which
is a ZR431 voltage reference in the example shown. The calibration
circuit further includes MOSFET Q1 for establishing the output
voltage VCO-IN of the calibration section 60, as described more
fully below.
The inputs VCO_CAL, and FETCAL to the calibration circuit 60 are
digital signals from the microcontroller 72 of the control section
70, as indicated in FIG. 8. When VCO_CAL, is at logic 0, the VREF
pin of voltage reference 62 is held low, effectively removing the
voltage reference 62 from the circuit and allowing resistors R7 and
R8 to form a voltage divider to the VCO circuit 50 directly from
the raw input voltage INPUT. When VCO_CAL is configured as an input
(high-impedance), the voltage reference 62 is turned "on", and the
input INPUT has no substantial effect on the voltage input to the
VCO circuit 50. Further, when the voltage reference 62 is turned
"on", one of two fixed calibration voltages is applied to the
calibration circuit output VCO_IN. The calibration voltage output
VCO-IN depends on the state of the signal FETCAL from the
microcontroller 72, as will now be described.
When the voltage reference 62 is turned "on", it modifies its
output VZ in order to maintain a fixed voltage at its VREF pin. In
one example, the fixed voltage at VREF is maintained at 2.5V when
the voltage reference 62 is turned "on". When the signal FETCAL
from the microcontroller 72 is set to logical 0, the MOSFET Q1 of
the calibration circuit 60 is turned "off", and no current flows
through resistor R5. This causes resistors R3 and R4 to establish
the output voltage VCO-IN from the calibration circuit 60. That is,
when the voltage reference 62 is turned "on", a voltage of 2.5V is
applied across resistor R4. The pin VREF of the voltage reference
62 then draws very low current so that essentially all of the
current set up in resistor R4 up goes through resistor R3. The
voltage at resistor R3 is therefore the sum of 2.5 Volts plus the
voltage calculated from the formula V=IR, where I is the current in
resistor R4, and R is the resistance of resistor R3. VZ will
therefore be equal to 2.5+(R4/2.5)*R3.
When the signal FETCAL, from the microcontroller 72 is set to
logical 1, the MOSFET Q1 of the calibration circuit 60 is turned
"on", and the reference voltage VREF from the voltage reference 62
(which will be 2.5V in the example being discussed) is applied
across the parallel combination of resistors R4 and R5. In this
instance, the output voltage VZ of the voltage reference 62 is the
sum of 2.5V plus the voltage calculated from the formula
((R4.vertline..vertline.R5)/2.5)*R3. A small amount of current is
used to turn on the transistor chain comprised of transistors Q4
and Q5. This transistor chain is configured to provide any current
necessary to brine VCO_IN up above the desired calibration voltage
so that the voltage reference 62 can perform properly.
In summary, the calibration circuit 60 is configured to supply
three output voltages VCO-IN voltages to the VCO circuit 50: two
fixed voltages and one which is directly variable with system input
voltage INPUT. This is accomplished by using resistors R7 and R8 of
FIG. 5 to divide the input voltage INPUT which is then provided to
the VCO circuit 50, which in turn generates a frequency based on
that voltage and feeds the generated frequency back to the
microcontroller 72, as indicated in FIG. 8. The VCO circuit 50
input voltage VCO-IN is set to one of two fixed calibration
voltages or a third voltage dependent on the input voltage software
the microcontroller 72, as will be described further below. With
these three points, the input voltage INPUT from the battery being
monitored can be calculated with accuracy.
The values and selection of the particular circuit components for
the VCO calibration circuit 60 shown in FIG. 5 are exemplary only.
In one variation on the calibration circuit 60 shown in FIG. 5, the
MOSFET Q1 can be eliminated by tying resistor R5 directly to the
micro port (shown as resistor R17 in the diagram).
Control Section
Turning to FIG. 8, in the embodiment shown a control section 70
coordinates the interaction of the various other components of the
DC energy source monitor 10, including the driving of the display
40, the signaling to the calibration circuit 60, and the receipt of
the output VCO-OUT from the VCO circuit 50, which output is
indicative of the voltage of the battery being monitored, as well
as the nominal voltage of the DC source being monitored. The
control section 70 is preferably driven by a programmable control
device, such as a microcontroller, a microcomputer, or a
microprocessor circuit. The programmable control device preferably
includes random access memory (RAM), read only memory (ROM), a
computation component configured to perform mathematical
calculations, and a counter configured to count pulses. A series of
machine executable steps can be stored in the ROM or can be loaded
into RAM from an external source for execution by the programmable
control device. In the DC energy source monitor application
described herein, a microcontroller is sufficient to provide the
minimum control functions, and a more complex microprocessor or
microcomputer is typically not justified. The discussion below will
assume that a PIC12C5XX microcontroller is used as the programmable
control device in the control section 70.
Turning to FIG. 6, a schematic diagram showing the connections to
the microcontroller 72 of the control section 70 is shown. The
microcontroller 72 receives as an input the square wave output
VCO_OUT of the VCO circuit 50, as shown in FIG. 8. Using internal
timers in the VCO circuit 50, such as capacitor C2 of FIG. 4, the
number of edges in a predetermined time frame are counted by the
microcontroller and the result is stored in the microcontroller as
a the value `y`. In one embodiment the predetermined time frame is
65.536 milliseconds.
The control section 70 is configured to determine the transfer
function of the VCO section 50. In one embodiment, this is
accomplished by using the two calibration voltages from the VCO
calibration section 60, as described above. Once the transfer
function has been established, the microcontroller 72 can then
determine overall system input voltage INPUT, and can then generate
a digital output to the display section to display the correct LEDs
to indicate the relative percent of charge and the nominal source
voltage, as described above.
The general calculations to be performed by the microcontroller 72
to achieve the calibration of the VCO section 50 as shown and
described more fully below. In operation, the control unit 70
periodically recalibrates the VCO section 50 via the calibration
unit 60 by reading new y1 and y2 values, as will be more fully
described below. These y1 and y2 values are used to determine new
values for the coefficients m and b for the equations shown below.
Note that the constants `c` and `x1` are fixed in software, as for
example by storing them in the microcontroller ROM. With the
periodically recalibrated m and b values, the controller 72 simply
reads a new y3 value, processes it using equation (7) below, and
obtains a value for x3, and uses x3 to set the appropriate LEDs to
indicate system input INPUT.
The calculations to be performed by the microcontroller 72 will now
be shown and described.
Recall that the output of the VCO circuit 50 is linear and of the
form y=m*x+b, where x is the input voltage VCO-IN, and y is the
output frequency VCO-OUT. The coefficients m and b can become
unstable over time, and therefore are preferably recalculated
periodically to maintain an accurate output y from the VCO circuit
50.
We start with the following equations:
To solve for m, subtract Eqn 2 from Eqn 1, i.e.,
(y1=m.multidot.x1+b)-(y2=m.multidot.x2+b). Solving for m, we
get
As described above in the for the calibration section 60, outputs
VCO-IN of the calibration circuit, which are the inputs x1 and x2
to the VCO circuit 50, are predetermined constants from circuit
analysis, and are thus known. The values y1 and y2, the output
frequency of the VCO section 50, are read by the microcontroller
72, and are thus also known. Thus, the quantity (-x1+x2) in Eqn. A
is a constant, which we will call "c", i.e.:
Thus, Eqn. A simplifies to
Solving Eqn. 1 for b, we see that
Now that the transfer function y=m*x+b of the VCO section 50 is
characterized in terms of two input voltages x1 and x2, we can
determine an arbitrary input voltage x3 given its corresponding
output y3. That is, if we know an input voltage VCO-IN of x3 to the
VCO circuit 50, we can calculate the output voltage measure VCO-OUT
of y3 by the formula
Solving Eqn. 6 for x3, we get
The microcontroller is thus programmed with a set of machine
executable steps to calculate m, b and x3 given the known or
measured values for y2, y1, x2, x1 and c.
Machine Executable Steps
As described above, the programmable control device 72 of FIG, 6
can be provided with a set of machine executable steps (i.e., a
program) to perform the calculations described in the previous
section. Turning to FIG. 7, an exemplary flow chart diagram of one
such set of computer executable steps is shown.
Turning now to FIG. 7, the voltage monitor of the present invention
is powered-up in step S1 by connecting it to a power source, such
as the power supply 30 of FIG. 2. In step S2, the values of y1 and
y2 (VCO-OUT of the VCO circuit 50) are generated by the VCO circuit
50 by providing known inputs VCO-IN of x1 and x2 to the VCO circuit
from the from the calibration section 60 in the manner described
above. In step S3, y1, y2, x1 and x2 are used to calculate values
for m and b using Eqns. 3 and 4.
In step S4, the calibration circuit 60 is put off-line, and input
VCO-CAL from the microcontroller 72 to the calibration circuit 60
is set to logical zero (i.e., to zero volts). Thereafter, in step
S5, a VCO-OUT signal y3 from the VCO section 50 is measured by the
microcontroller 72. Signal y3 is generated by applying the input
INPUT from the DC source being monitored to the calibration section
60 to generate VCO-IN of x3, which in turn generates VCO-OUT signal
y3 in the VCO section 50. Then, in step S6, x3 is calculated using
the measured value of y3 and the previously determined values of m
and b from step S3.
Following calculation of x3 in step S6, in step S7 the
microcontroller determines whether x3 represents a new DC energy
source type (i.e., does it fall outside of a predetermined range of
voltages associated with the nominal voltage of a DC source
immediately previously detected by the monitor, if any). If x3 does
not represent a new DC source type, then in step S9 the
microcontroller causes the display to indicate the relative level
of charge of the DC source. If a new nominal voltage is represented
by x3 in step S7, then the microcontroller causes the display to
indicate the DC source type (nominal voltage), and processing is
resumed at step S1.
If no new source type is indicated by x3 in step S7, then after
displaying the source relative charge level in step S9, the program
continues to step 510, In step S10, the microcontroller determines
if 250 milliseconds has elapsed since the last calibration, using a
clock, preferably an internal clock, to monitor the passage of
time. If 250 ms has not elapsed since the last calibration, the
program proceeds to step S5, and the VCO circuit output VCO-OUT is
measured, and processing continues from step S5 as described. If
250 ms or more has elapsed since the last calibration as measured
in step S10, then the microcontroller returns to step S2 to
generate known voltages to the calibration section, so that values
of m and b can be recalculated in the manner described.
The programmable control device 72 of the monitor 10 is further
provided with a look-up table of voltages appropriate to the range
of voltages anticipated to be encountered by the monitor. For
example, for a energy source monitor intended to monitor batteries
having nominal voltages of A, B and C, a table is provided
indicating that the range of voltages (lowest to highest) of A is
from A1 to A2, the range of voltages of B is from B1 to B2, and the
range of voltages of C is from C1 to C2 wherein A2<B1, and
B2<C1 . If a voltage is detected between A1 and A2, then the
microcontroller determines from the look-up table that the source
has a nominal voltage of A, and signals this to the display.
Further, if the microcontroller measures the voltage as A3, then
the microcontroller determines the battery charge from a look-up
table.
The look-up table of threshold values (i.e., when the battery is
deemed to pass from one remaining life level to another, for
example, the point at which the monitor indicates life has passed
from the "50%" level to the "25%" level) can either be set in the
ROM of the microcontroller, or can be set by a user of the monitor.
Similarly, the points at which a source is considered to become a
different nominal source can be set in ROM or can be set by a user
of the monitor. Likewise, state-of-health parameters can either be
set in ROM or user-defined in the manner described below. For
example, the point where the microcontroller specifically switches
from an indication of 75% to an indication of 100% can be at 12.1v
or programmed later to be at 12.23v. In another example, the
specific DC sources being monitored can be set initially as 6v,
12v, 24v, 36v, and 48v batteries, but later reprogrammed for 6v,
12v, 24v, 32v, and 48v batteries.
Turning to FIG. 9, a circuit schematic of a prior art battery
monitor 100 is shown. V1 represents the battery being monitored by
the monitor 100, while diode D101 provides reverse battery
protection and capacitor C101 provides power supply filtering. The
thresholds at which the monitor determines that the life of the
battery has passed from one stage to another are set in ROM of the
microcontroller.
Turning to FIG. 10, a schematic circuit diagram is shown which
allows a user of the monitor of the present invention to reprogram
the threshold values in the manner described above. In the circuit
of FIG. 10, a serial communication stream to send signals to the
microcontroller to change threshold levels has been added. A DC
blocking capacitor C202 is attached to an input port on the
microcontroller in the monitor 10. Source V2 is shown as an AC
source which is added in series with a fixed DC voltage source 9.
Diode D201 and capacitor C201 serve as a low pass filter to prevent
the AC component from being seen by the power supply circuitry of
the monitor 10. Capacitor C202 acts to block the DC power supply
voltage from source 9 thus only the signal with which is intended
to be communicate to the microcontroller is actually present at the
input port. This provides a one way communication path to the
microcontroller in the monitor 10. Using this communication path,
or serial communication stream, the microcontroller can be
reprogrammed to adjust the thresholds values at which nominal
voltages, percents of relative charge, and/or state-of health
parameters will be indicated by the display.
Source State-of-Health Monitor Module
Referring to FIG. 8, a source "state of health" module 80 can be
provided to the monitor 10 of the present invention. A typical
parameter of the state of health of the source to be monitored is
the conductance of the source. In addition, state-of-health can be
indicated by the capability of the source to accept instantaneous
current supply, the age of the source, and the charge capacity of
the source, which can also be monitored. In FIG. 8, capacitor C81
is used to provide direct current rejection, and resistor R82 acts
as a current shunt. An alternating current signal 84 is provided to
the conductance module 80, and the responsive signal is provided to
the A/D converter 86 which provides a digital output signal
indicative of the conductance of the source. The output of A/D
converter 86 is provided to the microcontroller. The difference
between the signal for the A/D converter 86 and the A/C input 84 is
indicative of the conductance of the source, and can be compared to
a look-up table stored into the microcontroller to determine the
relative conductance of the source as compared to a "healthy"
source of equivalent nominal voltage. The microcontroller module 70
of FIG. 8 can then display the result via display module 40.
In addition, the microcontroller can be programmed with a series of
machine executable steps to use the measured conductance of the
source to calculate the capability of the source to accept
instantaneous current, the age of the source, and the charge
capacity of the source. These calculated values can then be
compared to other look-up tables stored into the microcontroller to
determine their relative values as compared to preselected values
indicative of a "healthy" source of equivalent nominal voltage.
The Method
The invention further includes a method for determining a nominal
voltage of a battery. Using the charge on the battery. The method
includes providing a programmable control device having stored
ranges of numbers, each range corresponding to an associated
nominal battery voltage. The programmable control device further
includes a series of machine executable steps for comparing a
received signal to the stored ranges of numbers to identify an
associated nominal battery voltage. The charge on the battery is
measured, and a signal is generated using the measured charge. The
signal is then provided to the programmable control device. The
programmable control device uses the signal to identify the
associated nominal voltage based on the stored ranges of numbers,
and provides an output indicative of the nominal voltage of the
battery.
The method further includes the step of using a voltage controlled
oscillator to generate the signal which is provided to the
programmable control device. The method can further include the
step of periodically calibrating the voltage controlled oscillator
("VCO") to account for variations over time and between
oscillators. Preferably the calibration is done automatically. One
method of periodic automated calibration is to have the
programmable control device (generate a periodic, known signal.
This signal is then provided to the VCO, and the resulting output
from the VCO is measured and compared with the known signal
generated by the control device. The control device can then
provide a calibration signal. The signal can be provided to the
VCO, or it can be provided internally to the control device in the
series of machine executable steps which are provided to allow the
control device to calculate the battery charge from the signal.
More preferably, where the calculation of the VCO is performed by a
transfer function within the programmable controller, the
programmable controller is configured to generate as many known,
periodic signals of different values as there are variables in the
transfer function. For example, where the transfer function is
based on the equation y=mx+b, and x is an input signal to the VCO
and y is the output from the VCO, the coefficients m and b are
considered to be the variables which need to be determined for
calibration of the VCO. Therefore, two signals for x are generated,
and the corresponding y values are used to solve the two equation
problem y1=m.multidot.x1+b, and y2=m.multidot.x2+b.
While the above invention has been described with particularity to
specific embodiments and examples thereof, it is understood that
the invention comprises the general novel concepts disclosed by the
disclosure provided herein, as well as those specific embodiments
and examples.
* * * * *